1. Field of the Invention
The present invention relates to voice decoding. More particularly, the present invention relates to a method and apparatus of suppressing voice noise in a voice decoder.
2. Description of the Related Art
The term “vocoder” refers to a device that functions as both a voice encoder and a voice decoder. The vocoder is configured to transmit data including parameters generated by analyzing the characteristics of a voice signal and to synthesize speech based on parameters of received data.
Data transmitted over a communication network, particularly a wireless communication network that transmits and receives signals on radio channels or an Internet Protocol (IP) network, may be received with transmission errors due to a radio propagation environment. Therefore, a vocoder that is used in such a mobile communication environment generally has a speech synthesizing function that suffers a transmission/reception error environment and creates an output that is unperceivable to a user.
Accordingly, the vocoder typically includes an Error Concealment Unit (ECU) block that operates upon generation of an error in received data. In general, a channel decoder determines whether received packet data has an error by checking the Cyclic Redundancy Check (CRC) of the packet data and outputs a Bad Frame Indicator (BFI) indicating the CRC check result. The vocoder determines whether to operate the ECU block based on the BFI.
The ECU block increases the level of perceivable sound quality by repeating the audio signal of a previous frame or interpolating between a current frame and a previous frame depending on whether received packet data has an error. That is, the vocoder may reuse the audio signal of a previous frame transmitted with high quality or generate a new audio signal by interpolating between a high-quality audio signal and a low-quality audio signal.
In a low-quality wireless environment, the probability of generating a false alarm may be increased during decoding at a channel decoder. Upon generation of a false alarm, the vocoder may synthesize speech using abnormal packet data or may perform an unnecessary ECU operation on normal packet data. Moreover, the ECU operation of repeating a previous audio signal or interpolating between signals causes modulation noise, which in turn further degrades the sound quality. Accordingly, if the decoding performance of the channel decoder does not satisfy at least a predetermined level, speech is not synthesized normally with an ECU block.
Therefore, a need exists for an improved apparatus and method for suppressing vocoder noise in a low-quality wireless environment
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.